Two recent studies have demonstrated no improvement in hemodynamic parameters or survival following
naloxone administration in
hemorrhagic shock. This finding is in contrast to those of earlier studies, which consistently demonstrated a beneficial effect. The current study evaluated
naloxone's ability to improve hemodynamics when administered following a fixed-volume
hemorrhage, during a period of partial hemodynamic compensation. Thirteen conditioned beagles were anesthetized with
pentobarbital (25 mg/kg intravenously), endotracheally intubated, and instrumented with a femoral
arterial line and a pulmonary artery thermodilution
catheter. Animals were then subjected to an estimated 50% graded
hemorrhage (45 ml/kg) over one hour. Following
hemorrhage, animals were observed for 90 minutes, then reinfused with shed blood over 30 minutes, and finally observed for an additional 60 minutes. Six animals received
naloxone (2 mg/kg intravenously) 30 minutes after completion of
hemorrhage and then 2 mg/kg/hr for the duration of the study. Seven control animals received an equivalent volume of saline. Heart rate, mean arterial pressure, central venous pressure, cardiac output, arterial and mixed venous blood
gases, and serum
lactate level were measured at regular intervals throughout the study. Cardiac index and systemic vascular resistance index were calculated at the same intervals. Overall, there were no statistically significant differences in the mean data values for mean arterial pressure, cardiac index, systemic vascular resistance index, or
lactate, although
lactate values were consistently higher in the
naloxone group (two-tailed independent Student's t test). We conclude that
naloxone does not significantly improve hemodynamics when administered after a fixed-volume
hemorrhage.